Frame marking RTP header extension (PART 1: implement extension)

Bug: webrtc:7765
Change-Id: I23896d121afd6be4bce5ff4deaf736149efebcdb
Reviewed-on: https://webrtc-review.googlesource.com/85200
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Reviewed-by: Sergey Silkin <ssilkin@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24695}
diff --git a/modules/rtp_rtcp/source/rtp_video_header.h b/modules/rtp_rtcp/source/rtp_video_header.h
index 6c7a150..68b4884 100644
--- a/modules/rtp_rtcp/source/rtp_video_header.h
+++ b/modules/rtp_rtcp/source/rtp_video_header.h
@@ -13,6 +13,7 @@
 #include "absl/container/inlined_vector.h"
 #include "absl/types/variant.h"
 #include "api/video/video_content_type.h"
+#include "api/video/video_frame_marking.h"
 #include "api/video/video_rotation.h"
 #include "api/video/video_timing.h"
 #include "common_types.h"  // NOLINT(build/include)
@@ -56,6 +57,7 @@
 
   PlayoutDelay playout_delay;
   VideoSendTiming video_timing;
+  FrameMarking frame_marking;
   RTPVideoTypeHeader video_type_header;
 };